The present invention relates to a disc drive system. In particular, the present invention relates to a head positioning system capable of accommodating ever higher areal density of computer discs.
Disc drive systems are well known in the art and comprise several discs, each disc having concentric data tracks for storing data. The discs are mounted on a spindle motor, which causes the discs to spin. As the discs are spinning, a slider suspended from an actuator arm “flies” a small distance above the disc surface. The slider carries a transducing head for reading from or writing to a data track on the disc.
In addition to the actuator arm, the slider suspension comprises a bearing about which the actuator arm pivots. A large scale actuator motor, such as a voice coil motor (VCM), is used to move the actuator arm over the surface of the disc. When actuated by the VCM, the slider can be moved from an inner diameter to an outer diameter of the disc along an arc until the slider is positioned above a desired data track on the disc. Called tracking, this method of positioning the slider above the desired track on the disc allows the transducing head on the slider to either read from or write data to a selected track on the disc.
The areal recording density of the disc is typically given in tracks per inch (TPI). There is constant pressure to increase the areal density of discs, and thus increase the number of tracks per inch on the disc. As the tracks per inch increase, the accuracy of the system used to position the transducing head above the desired track on the disc must increase in proportion. This requires increasing the bandwidth of the servo system used to position the actuator arm.
There are many sources of error which reduce the track positioning accuracy of current slider suspension systems. The actuator arm is designed to be flexible to improve the ability of the slider to more closely follow the surface of the disc. However, this flexibility can result in the occurrence of unwanted resonances in the suspension as the suspension is moved across the disc surface during tracking. These unwanted resonances in the suspension reduce the ability to accurately control the slider positioning system at the required frequency. In addition, forces acting at the VCM, the bearing, and the actuator arm may all introduce potential error into the final tracking ability of the slider by adding to the resonance experienced in the actuator arm.
In an attempt to manage the amount of resonance in the suspension, secondary microactuators have been placed between the suspension and the slider. Moving the slider directly by using a form of microactuator has reduced, but has not eliminated the effect of suspension resonances. In particular, as the actuation force is applied to the slider by the microactuator, an equal and opposite reaction force is applied to the suspension, which in turn can create other resonance disturbances in the suspension. Control systems have been developed which attempt to compensate for the resonance and vibration experienced by the slider. However, such attempts reduce, but do not eliminate the effect of suspension resonances.
Microactuators and control systems have improved the tracking accuracy of sliders to where areal densities of up to 200,000 TPI may be possible. However, current goals are for discs having areal densities of as high as 500,000 to 1,000,000 TPI. At such areal densities, current slider positioning methods become inadequate.
Thus, there is a need in the art for an improved head positioning system which is capable of accommodating discs with ever higher areal densities.